Cylinder by-pass is the most common report received from the field, and a careful check is required to diagnose the problem.

  • Extend cylinders to the re-phasing position and lower hydraulics approximately 2″ (51 mm).
  • Then immediately disconnect the hydraulics from the tractor.
  • Measure the length of the extended cylinder rod on each cylinder.
  • Leave implement to stand for some hours, i.e. 3 hours.
  • Re-measure length of rods again and compare before and after measurements.
    Important: Some variation can be expected if implement is left for some time, i.e. overnight – due to change in temperature. Typically an implement set-up in the warmth of the afternoon may result in cylinder contraction of 5/8″ (16 mm) by next morning due to temperature change alone. Therefore, when reporting suspected leaking cylinders, the measurements must be at similar temperatures to give sensible results.
  • By analyzing the measurements obtained it can usually be established which is the suspect cylinder or cylinders. Please note that it is quite likely that some will retract while others will extend. In general, if in a static test, isolated from the tractor, a cylinder crept at a rate exceeding 1/16″ /hr (2 mm/hr) measure on the rod, assuming temperature is constant, then it requires attention to determine the cause.
  • When the ‘suspect’ cylinder has been identified, it is important that disassembly is carried out in a clean environment. The scoring of barrels and piston seals will usually indicate contamination of some type has entered the system.

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If one or more cylinders after re-phasing creep down more than others or the system is ‘spongy’ it is possible that air is present in the circuit. Check for air bubbles by removing the return line and catching oil in a clean container. With the rod clevises disconnected and the cylinders in as near as possible to vertical, hold in the re-phasing position until no aerated oil flows. The tractor should be run on low idling speed to minimize heat build up during the purging operation.

Important: Check tractor oil levels when carrying out this exercise. Once the air has been purged from the system it can only re-enter the system if the lines are cracked, removed, replaced, or the tractor oil level becomes very low.

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Over a period of time (i.e. 2 hours working) the phasing cylinders may become unbalanced due to small amounts of seal by-pass. To re-phase the cylinders it is necessary to extend them to the re-phasing position of approximately thirty (30) seconds to a minute. Retract and then extend the cylinders to ensure that they are stroking evenly and in phase with each other.

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